1. Field of the Invention
This invention relates to magnetic bubble domain systems, in general, and to relatively high yield, large capacity major/minor loop bubble domain memories, in particular.
2. Description of Prior Art
With the introduction of magnetic bubble domains, many devices have been developed. As these devices have been refined and improved, the bubble domain concept has progressed beyond the curiosity stage and into the realm of commercial utilization. To improve the utilization prospects, more and better systems and system applications are being inventigated and established. Some of the system applications include storage means such as memories.
In a bubble memory system, it is desirable to obtain maximum storage per individual chip in order to reduce the number of chips utilized. Where data storage capacity is the prime consideration and access time is of secondary importance, the total capacity of the individual memory chip is increased so that fewer chips are required. See, for example, copending application, Ser. No. 689,313; entitled Large Capacity Bubble Domain Memory with Redundancy, by T. T. Chen and I. S. Gergis; filed on May 24, 1976; assigned to the common assignee; and incorporated herein by reference. The utilization of smaller numbers of chips permits lower packaging and electronics costs as well as better system reliability. However, where increased throughput (or reduced access time) is desirable, the major-minor loop configuration is advantageous. This configuration permits the memory system to be arranged in smaller segments which can be accessed more quickly. In addition, certain access operations can be performed in parallel to increase operating speed and to reduce access time for information retrieval.
Presently known chip design capabilities use a basic memory cell which is processed photolithographically. The size of the cell is limited by the basic size of the mask which can be properly handled by the photoreduction process. Therefore, to increase the capacity of the chip, it is necessary to increase the storage density of the mask which is limited by the resolution of the photolithographic technique.
At present, bubble domain technology permits processing of a large number of memory cells on a relatively large garnet wafer with reasonable yield. However, when an improved method and design of a storage cell is provided, a large number of interconnected cells can be placed on a wafer.